WASHINGTON – President Obama's new grass-roots advocacy group will target more than a dozen members of Congress with online ads this week for failing to voice support for his plan to expand background checks to all gun buyers, organizers told USA TODAY.

The advertising push is part of a so-called national day of action planned Friday by Obama's backers to rally support for background checks. It will mark the first large-scale test of Organizing for Action's ability to mobilize the president's army of 2.2 million campaign volunteers to press for legislative change.

Obama and a group of his closest advisers launched Organizing for Action (OFA) in late January to transform his campaign operation into a tax-exempt group to advance his second-term priorities, including gun control, immigration and climate change.

Organizers did not disclose which lawmakers they would target in the first round of advertising but say they could spend as much as $100,000. The goal is to expand criminal background checks on all gun purchasers. The current system applies only to federally licensed gun dealers and excludes guns sold privately. In addition, OFA is sponsoring more than 100 events in more than 80 congressional districts across the country to demand congressional action.

"That's the strength the OFA will bring to supporting the president's agenda," said Jon Carson, the group's executive director and the former director of the White House office of public engagement. "We have voices in every corner of this country who are supporting his agenda and can make their neighbors understand where their members (of Congress) stand on these important issues."

The push for background checks is just one part of the president's sweeping plan to rein in gun violence in the wake of the school shooting massacre Dec. 14 in Newtown, Conn. Carson said OFA backs the full package, which includes renewing the ban on assault weapons and limiting ammunition magazines to 10 rounds.

Carson said the group is starting the push with background checks because there's broad support for the issue. A Quinnipiac poll released this month found 92% of voters supported universal background checks, and a bipartisan group of senators is working on legislation to close loopholes in the system.

It's hard to get reliable data on private gun sales. The White House and gun-control groups have estimated that 40% of gun purchases are not covered by the background checks system.

"There's an education process for people," Carson said. "Many people don't know what the loophole is."

Obama's decision to establish a separate advocacy group, organized as a social welfare organization under the U.S. tax code, is an unprecedented move for a sitting president. In earlier presidencies, that task might have been performed by the Democratic National Committee or a political office within the White House. A precursor operation, Organizing for America, operated within the DNC during the president's first term. "We are going to be 100% focused on issue campaigns, and we won't be doing any candidate-specific electoral politics," Carson said.

Rather than relying on building coalitions of unions and like-minded environmental and liberal groups to advance his agenda, "the president is essentially creating his own lobbying entity," said Anthony Corrado, a professor of government at Colby College in Maine.

Unlike the Democratic Party, which faces strict campaign contribution limits, Organizing for Action will take unlimited money from corporations, unions and individuals. That will free it to raise big sums quickly to mount aggressive, campaign-style grass-roots and advertising efforts.

Campaign-finance watchdogs, such as Democracy 21 President Fred Wertheimer, have slammed the decision as a "dangerous" precedent that will allow special interests to curry favor with the administration.

Jim Messina, Obama's 2012 campaign manager and OFA chairman, said the group will not accept money from political action committees or federal lobbyists.

Corporations may back the group's efforts on immigration, Messina said, but he expects much of the financial support to come from donors who give in small amounts.

"This grass-roots movement is going to be funded just like the campaign was," Messina said. "Our average contribution was $51."

The group plans to disclose donors every three months and report contributions in broad ranges.

Strictly political tasks will fall to the Democratic National Committee, which will work to help elect more Democrats to Congress in next year's midterm elections. Obama has committed to hold at least 14 fundraisers this year to help Democratic candidates get to the House and Senate, Roll Call reported this month.

Carson and other key staffers are working in downtown Washington. By June, OFA will finish relocating its operations to Chicago, the president's hometown. Carson said staffing levels and budget are being decided, but "we will have a pretty robust organization to support the president's agenda."

The goal is to create an organization that survives past Obama's presidency. "This is a network of people who want to fight for progressive change in their communities," Carson said. "I can see it evolving over time."

Supporters organized 1,200 house parties to watch Obama's State of the Union, and 19,500 joined a "tele-townhall" to discuss the president's job proposal with Chicago Mayor Rahm Emanuel and others. "We feel very good about the early signs," Carson said.

OFA spokeswoman Katie Hogan and Carson said they expect thousands to participate in Friday's events, which include letter-writing campaigns, vigils and news conferences.

New Yorker Alan Howard is helping organize a candlelight vigil Friday evening on Staten Island to draw the attention of Rep. Michael Grimm, R-N.Y. Howard, 72, volunteered for Obama's first campaign and worked on the re-election. He said he hasn't slowed down since the election, juggling about 30 hours a week of OFA volunteer activities with his work as a consultant to international labor rights groups.

"What's we're really working at is transforming that coalition that elected Obama into a movement," he said. "That's a very exciting prospect for many of us."

A spokeswoman for Grimm did not immediately respond to an interview request.